Update startDescent function to hide the start button during descent transition. This change prevents the button from capturing pointer events and allows user interactions with underlying elements, ensuring a smoother experience.

frontend/main.js

@@ -550,12 +550,10 @@ function startDescent() {
   intro.phase = "descending";
   intro.t0 = performance.now();
   overlay.classList.add("hidden");
-  // The overlay fades via opacity (no display:none, to keep the exit
-  // transition), but #start-btn.ready stays pointer-events:auto — leaving an
-  // invisible button pinned at screen center that swallows clicks on whatever
-  // sits under it (the bench / cassette collection). Drop .ready so the spent
-  // button stops capturing pointer events.
-  startBtn.classList.remove("ready");
+  // The overlay only fades out (opacity), so its still-`ready` start button
+  // would stay pinned on top and swallow clicks meant for the scene behind it
+  // (e.g. the bench / cassette collection). Hide the spent button outright.
+  startBtn.hidden = true;
 }
 
 const pageLoaded = new Promise((resolve) =>